Small boat

ABSTRACT

A small boat includes engines mounted on a hull, a plurality of water jet propulsion units disposed on both sides of a longitudinal axis of the hull and driven by the engines, and a steering wheel arranged to change jet directions of the water jet propulsion units. The small boat further includes a steering angle sensor arranged to detect a rotational angle of the steering wheel, front and rear gravity sensors arranged to detect a turning state of the hull, and a control device to which the rotational angle and the turning state of the hull are inputted in order to control thrusts of the water jet propulsion units such that the turning state coincides with any one of a group of target steady turning radii corresponding to the rotational angle of the steering wheel. The small boat turns along the steady radius regardless of any water conditions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a small boat including a plurality of water jet propulsion units disposed on both sides of a longitudinal axis of a hull and arranged to be driven by engines on the small boat. The running direction of the hull is changed by adjusting water jet directions of the water jet propulsion units.

2. Description of the Related Art

In some conventional small boats, two inboard-outboard motors are mounted to a hull (stern drive), and outputs of the left and right engines are controlled according to a rotational angle of a steering lever (steering handle) to improve turning performance (see JP-A-Hei 3-70697, for example).

In the case of the conventional small boat, the output control of the left and right engines is performed according only to the rotational angle of the steering handle. Therefore, even though turning performance is improved, an operator cannot turn a boat along his/her intended turning track without fine adjustments of the rotational angle of the steering handle. This occurs even if the rotational angle of the steering handle is constant because the actual turning track varies according to water conditions (waves, wind, tide, etc.).

Similarly, when running straight, even if the operator tries to maintain a straight path without turning the steering handle, the boat may not continue on the straight path due to the water conditions as described above.

In conventional boats with either an outboard or an inboard-outboard motor, because a propulsion unit protrudes below water, the propulsion unit more or less provides the same effect as a rudder. However, in small boats propelled by a water jet propulsion unit, the same rudder effect as described above cannot be obtained because of structural differences. Accordingly, when a boat is running at low speed for docking or the like, more precise accelerator operation and steering operation is required.

SUMMARY OF THE INVENTION

Accordingly, there is an unmet need in the art for making the operation of the boat during docking (running at low speed) easier.

In order to overcome the problems described above, preferred embodiments of the present invention provide a small boat which turns along a turning track intended by an operator regardless of the water conditions.

A preferred embodiment of the present invention is directed to a small boat including an engine mounted on a hull, a plurality of water jet propulsion units driven by the engine and disposed on both sides of a longitudinal axis of the hull, and a steering wheel arranged to change jet directions of the water jet propulsion units. The small boat preferably includes a steering angle sensor arranged to detect a rotational angle of the steering wheel, a running state detection device arranged to detect a running state of the hull, and a control device which detects the rotational angle of the steering wheel by analyzing the steering angle sensor and the running state of the hull detected by the running state detection device. Signals from the steering angle sensor and the running state detection device are used to control thrusts of the water jet propulsion units so that the running state coincides with a target running track corresponding to the rotational angle of the steering wheel.

In another preferred embodiment of the present invention, the control device is arranged to control thrusts of the water jet propulsion units when the control device determines that the hull is in a turning state based on the rotational angle of the steering wheel so that the actual turning state coincides with a target steady turning radius corresponding to the rotational angle of the steering wheel.

Another preferred embodiment of the present invention preferably includes a throttle device actuated by an operator to adjust an output of the engine, and a throttle position sensor arranged to detect a displacement of the throttle device, wherein the control device is arranged to establish a target steady turning radius based on the rotational angle of the steering wheel and the displacement detected by the throttle position sensor.

Another preferred embodiment of the present invention preferably includes a speed sensor arranged to detect a running speed of the small boat, wherein the control device is arranged to establish the target steady turning radius based on the rotational angle of the steering wheel and the running speed detected by the speed sensor.

In another preferred embodiment of the present invention the running state detection device preferably includes a gravity (G) sensor arranged to detect acceleration due to centrifugal force, and a plurality of the G sensors are provided along the longitudinal axis of the hull.

In a preferred embodiment of the present invention, one engine is preferably provided per one water jet propulsion unit.

A preferred embodiment of the present invention preferably includes a thruster provided on the hull arranged to generate a lateral thrust that crosses the longitudinal axis of the hull at a right angle or substantially at a right angle, wherein the control device controls the thrust of the thruster such that the running state coincides with the target steady turning radius.

In a preferred embodiment of the present invention, a plurality of the thrusters are preferably provided along the longitudinal axis of the hull.

Another preferred embodiment of the present invention includes an engine mounted on a hull, a plurality of water jet propulsion units driven by the engine and disposed on both sides of a longitudinal axis of the hull, and a steering wheel provided on the hull. The small boat preferably includes a steering angle sensor arranged to detect a rotational angle of the steering wheel, a running state detection device arranged to detect a running state of the hull, and a control device to which the rotational angle of the steering wheel detected by the steering angle sensor and the running state of the hull detected by the running state detection device are inputted to control a water jet direction of each of the water jet propulsion units such that the running state coincides with a target running track corresponding to the rotational angle of the steering wheel.

In a preferred embodiment of the present invention, the control device is arranged to control the water jet directions of the water jet propulsion units when the control device determines, based on the rotational angle of the steering wheel, that the hull is in a turning state such that the turning state coincides with a target steady turning radius corresponding to the rotational angle of the steering wheel.

A preferred embodiment of the present invention preferably includes a throttle device actuated by an operator to adjust an output of the engine, and a throttle position sensor arranged to detect a displacement of the throttle device, wherein the control device establishes the target steady turning radius based on the rotational angle of the steering wheel and the displacement detected by the throttle position sensor.

A preferred embodiment of the present invention preferably includes a speed sensor arranged to detect a running speed, wherein the control device establishes the target steady turning radius based on the rotational angle of the steering wheel and the running speed detected by the speed sensor.

A preferred embodiment of the present invention preferably includes a G sensor arranged to detect acceleration due to centrifugal force, and a plurality of the G sensors are preferably provided along the longitudinal axis of the hull.

A preferred embodiment of the present invention preferably includes a thruster provided on the hull arranged to generate a lateral thrust that crosses the longitudinal axis of the hull at a right angle, wherein the control device controls the thrust of the thruster such that the turning state coincides with the target steady turning radius.

Another preferred embodiment of the present invention preferably includes a plurality of the thrusters provided along the longitudinal axis of the hull.

In the preferred embodiments of the present invention, the running state includes running in either a straight or a turning direction and denotes how large the radius of an actual turning radius of a boat is when it is detected by the running state detection device. The radius of the detected turning radius is calculated, for example, from acceleration due to centrifugal force. As the acceleration increases, the boat is determined to be turning at a smaller radius. When the boat is running straight, its actual turning radius is infinite.

Further, the target steady turning radius denotes an ideal turning track which the hull is assumed to follow the rotational angle of the steering wheel as if there were no disturbances. It decreases as the rotational angle of the steering wheel increases and it increases as the rotational angle of the steering wheel decreases.

In addition, the controlling thrust of a water jet propulsion unit occurs when either (1) the thrust of the water jet propulsion unit is varied by controlling an engine output, or (2) the thrust of the water jet propulsion unit is controlled by changing a pitch of the blades in a jet pump or by changing a nozzle diameter of a jet nozzle. The thrust is controlled such that a turning radius in the running state coincides with the target steady turning radius.

According to a preferred embodiment of the present invention, the thrust of the water jet propulsion unit is controlled such that the running state of the hull coincides with a target track corresponding to the rotational angle of the steering wheel. Therefore, the boat can run along the target track intended by an operator. The small boat can also be driven along an intended track when the boat is running at low speed for docking or the like, thereby facilitating the docking operation.

According to a preferred embodiment of the present invention, when the hull is in a turning state, thrust of the water jet propulsion unit is controlled such that the turning state of the hull coincides with a target steady turning radius established according to the rotational angle of the steering wheel. Therefore, the boat can turn along a turning track intended by the operator regardless of the water conditions.

According to a preferred embodiment of the present invention, the target steady turning radius is established based on the rotational angle of the steering wheel and the throttle displacement. Accordingly, the radius of the target steady turning radius can be smaller relative to the rotational angle of the steering wheel as the throttle displacement becomes smaller. This allows the radius of a turning track to be made smaller relative to the rotational angle of the steering wheel in order to provide a smaller turning radius when the boat is running at low speed for purposes of docking or the like.

According a preferred embodiment of the present invention, the target steady turning radius is established based on the rotational angle of the steering wheel and the running speed detected by the speed sensor. Accordingly, the radius of the target steady turning radius can be larger than the relative rotational angle of the steering wheel when the running speed becomes faster. Because of this feature, the boat can turn smoothly when running at high speed thereby preventing an unpleasant lateral force from being exerted on the operator.

According to a preferred embodiment of the present invention, the turning state detection device is defined by providing a plurality of G sensors along the longitudinal axis of the hull arranged to detect acceleration due to centrifugal force. Accordingly, a location with respect to the target turning track for the small boat and a direction of the longitudinal axis of the hull can be detected. In other words, a posture of the hull with respect to the target steady turning radius can be detected. Using these detected values, the turning state of the hull can be made to precisely coincide with the target steady turning radius.

According to a preferred embodiment of the present invention, one engine is preferably provided per one water jet propulsion unit. Using this arrangement, each engine can be separately operated in order to easily control the left and right thrusts. Therefore, the actual turning state of the hull can be made to precisely coincide with the target steady turning radius.

According to a preferred embodiment of the present invention, the thruster arranged to generate a lateral thrust that crosses the longitudinal axis of the hull at a right angle is controlled such that the turning state coincides with the target steady turning radius. Thereby, turning control can be performed easily and reliably.

According to a preferred embodiment of the present invention, a plurality of thrusters are preferably provided along the longitudinal axis of the hull. By using a plurality of thrusters, the turning control can be performed easily and reliably.

According to a preferred embodiment of the present invention, an engine output and a water jet direction of the water jet propulsion unit are controlled such that the running state of the hull coincides with a target track corresponding to the rotational angle of the steering wheel. In addition, the engine output and the water jet direction of each water jet propulsion unit are controlled such that the actual turning state of the hull coincides with the target steady turning radius. Therefore, turning accuracy can be further enhanced as compared to a case in which the water jet direction is fixed according to the rotational angle of the steering wheel. Also, the small boat can be driven along an intended track when the boat is running at low speed for docking or the like, thereby facilitating the docking operation.

Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a jet boat according to a first preferred embodiment of the present invention.

FIG. 2 is a side view of the jet boat.

FIG. 3 is a block diagram of the jet boat.

FIG. 4 is an illustration for describing an operation of the boat.

FIG. 5 is a block diagram of a jet boat according to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention are described with reference to the attached drawings.

FIGS. 1 to 4 illustrate a jet boat (small boat) according to a first preferred embodiment of the present invention. FIG. 1 is a plan view, FIG. 2 is a side view, and FIG. 3 is a block diagram of the jet boat. FIG. 4 illustrates various operations of the boat.

In the drawings, reference numeral 1 denotes a jet boat. This jet boat 1 preferably includes, for example, a hull 2 preferably made of FRP (Fiber Reinforced Plastics); left and right engines 3, 4 mounted in an engine room 2 a of the hull 2; left and right water jet propulsion units 5, 6 disposed in a propulsion room 2 b and driven by each of the engines; and an electric bow thruster 13 a installed on the front portion of the hull 2 for generating a lateral thrust that crosses a longitudinal axis “A” of the hull 2 at a right angle.

In a cabin 2 c opened upward on the hull 2, a steering wheel 7, an operator's seat 8, an assistant's seat 9, and a passenger's seat 10 are provided. A throttle shift lever 11 is disposed on the right side of the operator's seat 8. Shifting between the forward and the reverse positions and power adjustment of the engines is performed by turning the throttle shift lever 11 in a fore-and-aft direction.

The left and right engines 3, 4 are disposed such that each of their crankshafts extend in parallel or substantially in parallel with the longitudinal axis “A” of the hull 2 on the left and right sides thereof. The left and right water jet propulsion units 5, 6 have left and right jet pumps 5 a, 6 a driven by the crankshafts of the engines 3, 4 and left and right jet nozzles 5 b, 6 b for jetting water discharged from the pumps in a rearward direction.

The left and right jet nozzles 5 b, 6 b are connected to the jet pumps 5 a, 6 a so as to be swingable around shafts 5 c, 6 c which extend vertically and are connected to the steering wheel 7 with a cable 12. The left and right jet nozzles 5 b, 6 b swing to the left and right by turning the steering wheel 7 to the left and right, thereby causing the water to be jetted in the left and right directions.

A front G sensor 17 and a rear G sensor 18 are respectively disposed in a front and the rear portion of the hull 2 and are arranged to detect a centrifugal force exerted on the hull 2. Additionally, a speed sensor 19 arranged to detect a running speed of the hull 2 is disposed at the stern. A steering position sensor 20 arranged to detect the rotational angle of the steering wheel 7 is attached to the steering wheel 7. The throttle shift lever 11 is provided with throttle position sensors 21, 22 for the left and right engines, respectively. Because the throttle position sensors 21, 22 for the left and right engines are both operated using the throttle shift lever, left and right throttle openings are preferably the same.

A control ECU 14 arranged to control the entire driving state of the jet boat 1 is disposed in the right side of the right engine 4. Left and right engine ECUs 15, 16 arranged to control the driving states of the left and right engines 3, 4 respectively are disposed on the engine room 2 a side of a bulkhead 2 d between the engine room 2 a and the propulsion room 2 b.

Detection values 17 a, 18 a of the front and the rear G sensors 17, 18 corresponding to the acceleration due to centrifugal force, a detection value 19 a of the speed sensor 19 corresponding to the running speed, and a detection value 20 a of the steering position sensor 20 corresponding to the rotational angle are inputted to the control ECU 14. For example, a target steady turning radius “R” is established based on the rotational angle of the steering wheel 7 input from the steering position sensor 20 and the running speed 19 a input from the speed sensor 19, and a turning state of the hull 2 is calculated based on the accelerations 17 a, 18 a due to the centrifugal force input from the front and the rear G sensors 17, 18 and the running speed 19 a input from the speed sensor 19.

In the present preferred embodiment, the target steady turning radius denotes an ideal turning track which is obtained, for example, when the boat runs on calm water without any disturbances with its steering wheel 7 turned to a certain rotational angle. Accordingly, as the rotational angle increases, the target steady turning radius becomes smaller. Conversely, as the rotational angle decreases, the target steady turning radius increases. In addition, if the rotational angle of the steering wheel is maintained at the same angle, the faster the running speed becomes, the larger the target steady turning radius becomes; while the slower the running speed becomes, the smaller the target steady turning radius becomes.

Also, in the present preferred embodiment, the actual turning state of the hull 2 denotes a point at which the hull 2 is located in the target steady turning radius and in which direction the hull 2 is directed. This direction is represented, for example, as the angle defined by the longitudinal axis “A” of the hull 2 and a tangent at that point.

The control ECU 14 outputs left and right engine control signals 14 a, 14 b, to the left and the right engine ECUs 15, 16. These signals are calculated such that the actual turning state of the hull 2 coincides with the target steady turning radius. The control ECU 14 also outputs a thruster drive signal 14 c to the bow thruster 13 a.

The target steady turning radius “R” is set, for example, to radius R1 with a small curvature radius as the rotational angle of the steering wheel 7 becomes larger and the running speed becomes lower. Conversely, the target steady turning radius “R” is set to radius R3 with a large curvature radius as the rotational angle of the steering wheel 7 becomes smaller and the running speed becomes faster.

Detection values 21 a, 22 a of the throttle position sensors 21, 22 corresponding to the throttle displacement are inputted to the left and right engine ECUs 15, 16 to control fuel injection amounts, fuel injection timing, ignition timing and so forth of the engines 3, 4. The engine control signals 14 a, 14 b from the control ECU 14 are given priority. As a result, outputs of the left and right engines 3, 4 are controlled such that the actual turning state of the hull 2 coincides with the target steady turning radius “R.”

Specifically, if the target steady turning radius is set, for example, to R1 based on the rotational angle of the steering wheel 7 and the running speed of the hull when the actual turning state of the hull 2 is determined to be deviated toward the R2 side, output control of the left and right engines 3, 4 is performed such that the output of the left engine 3 increases and the output of the right engine 4 decreases.

Thus, in the present preferred embodiment, the left and right jet pumps 5, 6 are separately driven by the left and right engines 3, 4, the target steady turning radius “R” is established based on the rotational angle 20 a of the steering wheel 7 and the running speed 19 a, and the actual turning state of the hull 2 such as its direction and location is detected to separately control the outputs of the engines 3, 4 so that the actual turning state coincides with the target steady turning radius “R.” Therefore, the boat can turn along a turning track as intended by the operator regardless of any water conditions.

In addition, the G sensors arranged to detect the actual turning state of the hull 2 are preferably provided at two locations, in the front and the rear portions of the hull. This allows one to reliably detect not only whether or not the hull 2 is positioned on the turning track but also a direction (posture) of the hull. As a result, control accuracy of turning can be enhanced.

Also, the target steady turning radius is established based on the rotational angle of the steering wheel and the running speed, which allows making the radius of the target steady turning radius small relative to the rotational angle of the steering wheel when the boat is running at low speed for docking or the like. Therefore, the jet boat 1 can be driven along an intended turning track when the boat is running at low speed for docking or the like.

Further, as the running speed increases, the radius of the target steady turning radius can be larger relative to the rotational angle of the steering wheel. Therefore, the boat can turn smoothly when running at high speed, which prevents an unpleasant lateral force from being exerted upon the operator.

Further, the bow thruster 13 a and a stern thruster 13 b are provided respectively on the front and the rear portion of the hull to be controlled such that the actual turning state coincides with the target steady turning radius, thereby further enhancing control turning accuracy.

Incidentally, the target steady turning radius is established based on the rotational angle of the steering wheel and the running speed in first preferred embodiment. However, the target steady turning radius may be established based on the rotational angle of the steering wheel and the throttle displacement or based on the rotational angle of the steering wheel, the running speed, and the throttle displacement.

In such a configuration as described above, as the throttle displacement decreases the radius of the target steady turning radius can be decreased relative to the rotational angle of the steering wheel. Accordingly, when the throttle displacement is small, as it is in docking or the like, the radius of the target steady turning radius (target turning track) becomes small relative to the rotational angle of the steering wheel, which allows a smaller turning radius and further facilitates docking operation.

In the first preferred embodiment, an error between the target steady turning radius and the actual turning state of the hull is corrected by the output control of the engines which in turn controls the thrust of the water jet propulsion units. However, the error may be corrected by directly controlling the thrusts of the water jet propulsion units 5, 6. For example, at least one of a suction amount of the left and right jet propulsion units 5, 6, a pitch of the blades, a diameter of the jet nozzle, etc. can be varied. Accordingly, the error can be corrected by controlling any one of the above variables. In this case, the effect may be achieved through only one engine.

FIG. 5 is a block diagram illustrating a second preferred embodiment of the present invention, in which similar or corresponding elements are denoted by the same reference numerals as those in FIG. 3.

In the first preferred embodiment, the jet nozzles 5 b, 6 b are mechanically connected to the steering wheel 7 with the cable 12. In contrast, in the second preferred embodiment, the left and right jet nozzles 5 b, 6 b include left and right nozzle actuators 5 d, 6 d. The nozzle actuators 5 d, 6 d are arranged to pivot the jet nozzles 5 b, 6 b about the shafts 5 c, 6 c.

In the first preferred embodiment, only the bow thruster 13 a is provided on the front portion of the hull. In contrast, in the second preferred embodiment, a stern thruster 13 b is additionally provided on the rear portion of the hull (shown by broken lines in FIG. 2).

The control ECU 14 outputs the engine control signals 14 a, 14 b to the left and right engine ECUs 15, 16 for allowing the actual turning state of the hull 2 to coincide with the target steady turning radius “R” and thereby controls the outputs of the left and the right engines 3, 4. In addition, the control ECU 14 outputs actuator control signals 14 e, 14 f to the left and right nozzle actuators 5 d, 6 d to thereby control water jet directions of the jet nozzles 5 b, 6 b. Further, the control ECU 14 outputs a thruster control signal 14 d to the stern thruster 13 b to control a lateral thrust by the thruster.

Specifically, if the target steady turning radius is set, for example, to R1 based on the rotational angle of the steering wheel 7 and the running speed of the hull, when the actual turning state of the hull 2 is determined to be deviated toward the R2 side, output control of the left and right engines 3, 4 is performed such that the output of the left engine 3 increases and the output of the right engine 4 decreases and the pivot angles of the jet nozzles 5 b, 6 b are controlled such that water jet directions are directed inward of the turning direction with respect to the longitudinal axis “A” of the hull 2.

In the second preferred embodiment, in order for the actual turning state of the hull 2 to coincide with the target steady turning radius “R,” control of water jet directions of the left and right jet nozzles 5 b, 6 b and the output control of the left and right engines 3, 4 are also performed. Therefore, control accuracy of turning can be enhanced when compared with a case in which the jet directions are fixed according to the rotational angle of the steering wheel. Furthermore, the bow thruster 13 a is provided on the front portion of the hull and the stern thruster 13 b is provided on the rear portion of the hull. Controlling thrust by both the thrusters 13 a, 13 b further enhances controlling the accuracy of turning.

In the present preferred embodiment, the turning control is described. However, a preferred embodiment of the present invention may also be applied when running straight, as shown by R0 in FIG. 4. When driving a boat, in spite of the steering wheel being kept in the straight position, the boat tends to be deflected from a straight track by water disturbances. However, using the control arrangement of the present preferred embodiment, it is possible to easily keep running on a straight track.

Specifically, in a case where the steering angle sensor detects that the rotational angle of the steering wheel is equal to zero, the running state detection device recognizes that the hull is running straight and the control device controls the thrust or the water jet direction of the water jet propulsion unit such that the boat traces a straight track.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A boat comprising: at least one engine mounted on a hull; a plurality of water jet propulsion units disposed on both sides of a longitudinal axis of the hull and driven by the at least one engine; a steering wheel arranged to change jet directions of the water jet propulsion units; a steering angle sensor arranged to detect a rotational angle of the steering wheel; a running state detection device arranged to detect a running state of the hull; and a control device arranged to receive the rotational angle of the steering wheel detected by the steering angle sensor and the running state of the hull detected by the running state detection device, and control thrusts of the water jet propulsion units such that the running state coincides with a target running track corresponding to the rotational angle of the steering wheel.
 2. The boat according to claim 1, wherein the control device is arranged to determine, based on the rotational angle of the steering wheel, that the hull is in a turning state, and control the thrusts of the water jet propulsion units such that the turning state coincides with a target steady turning radius corresponding to the rotational angle of the steering wheel as detected by the steering angle sensor.
 3. The boat according to claim 2, further comprising: a throttle device operable by an operator in order to adjust an output of the engine; and a throttle position sensor arranged to detect a displacement of the throttle device; wherein the control device establishes the target steady turning radius based on the rotational angle of the steering wheel and the displacement detected by the throttle position sensor.
 4. The boat according to claim 2, further comprising a speed sensor arranged to detect a running speed of the boat, wherein the control device establishes the target steady turning radius based on the rotational angle of the steering wheel and the running speed detected by the speed sensor.
 5. The boat according to claim 1, wherein the running state detection device includes a plurality of gravity sensors arranged to detect acceleration due to centrifugal force, the plurality of gravity sensors being provided along the longitudinal axis of the hull.
 6. The boat according to claim 1, wherein one of the at least one engine is provided per each water jet propulsion unit.
 7. The boat according to claim 1, further comprising a thruster provided on the hull and arranged to generate a lateral thrust that crosses the longitudinal axis of the hull at substantially a right angle, wherein the control device controls the thrust of the thruster such that the running state coincides with the target steady turning radius.
 8. The boat according to claim 7, wherein a plurality of the thrusters are provided along the longitudinal axis of the hull.
 9. A boat comprising: at least one engine mounted on a hull; a plurality of water jet propulsion units disposed on both sides of a longitudinal axis of the hull and driven by the engine; a steering wheel provided on the hull; a steering angle sensor arranged to detect a rotational angle of the steering wheel; a running state detection device arranged to detect a running state of the hull; and a control device arranged to receive the rotational angle of the steering wheel detected by the steering angle sensor and the running state of the hull detected by the running state detection device, and to control a water jet direction of each of the water jet propulsion units such that the running state coincides with a target running track corresponding to the rotational angle of the steering wheel.
 10. The boat according to claim 9, wherein the control device is arranged to determine, based on the rotational angle of the steering wheel, that the hull is in a turning state, and control the water jet directions of the water jet propulsion units such that the turning state coincides with a target steady turning radius corresponding to the rotational angle of the steering wheel.
 11. The boat according to claim 10, further comprising: a throttle device operable by an operator in order to adjust an output of the at least one engine; and a throttle position sensor arranged to detect a displacement of the throttle device; wherein the control device establishes the target steady turning radius based on the rotational angle of the steering wheel and the throttle displacement detected by the throttle position sensor.
 12. The boat according to claim 10, further comprising a speed sensor arranged to detect a running speed of the boat, wherein the control device establishes the target steady turning radius based on the rotational angle of the steering wheel and the running speed detected by the speed sensor.
 13. The boat according to claim 9, wherein the running state detection device includes a plurality of gravity sensors arranged to detect acceleration due to centrifugal force, and a plurality of the gravity sensors are provided along the longitudinal axis of the hull.
 14. The boat according to claim 9, wherein one of the at least one engine is provided per each water jet propulsion unit.
 15. The boat according to claim 9, further comprising a thruster provided on the hull and arranged to generate a lateral thrust that crosses the longitudinal axis of the hull at substantially a right angle, wherein the control device controls the thrust of the thruster such that the turning state coincides with the target steady turning radius.
 16. The boat according to claim 15, wherein a plurality of the thrusters are provided along the longitudinal axis of the hull. 